From d2486dd73b95f0130c095734794a1fa7ce707874 Mon Sep 17 00:00:00 2001
From: Norman Princen <nprincen@hotmail.com>
Date: Tue, 12 May 2020 10:25:01 -0700
Subject: [PATCH] Minimize SendTo and Read Socket Timeout Delays

SendTo and Read were using longer than necessary socket timeouts that may add to process time delay and stuttering.  They were also using different values between Window and Linux/Mac.  The timeouts are now standardized for all versions and coded in the same manner as the xplaneConnect.c functions.
---
 xpcPlugin/UDPSocket.cpp | 54 ++++++++++++++++++++++++++---------------
 1 file changed, 34 insertions(+), 20 deletions(-)

diff --git a/xpcPlugin/UDPSocket.cpp b/xpcPlugin/UDPSocket.cpp
index 6eaf3e1..440a6a6 100644
--- a/xpcPlugin/UDPSocket.cpp
+++ b/xpcPlugin/UDPSocket.cpp
@@ -56,22 +56,25 @@ namespace XPC
 			return;
 		}
 
-		// Set Timout
-		int usTimeOut = 500;
-
+		// Set timeout period for SendTo to 1 millisecond
+		// Without this, playback may become choppy due to process blocking
 #ifdef _WIN32
-		DWORD msTimeOutWin = 1; // Minimum socket timeout in Windows is 1ms
-		if(setsockopt(this->sock, SOL_SOCKET, SO_RCVTIMEO, (char *)&msTimeOutWin, sizeof(msTimeOutWin)) != 0)
+		// Minimum socket timeout in Windows is 1 millisecond (0 makes it blocking)
+		DWORD timeout = 1;
+#else
+		struct timeval timeout;
+		timeout.tv_sec = 0;
+		timeout.tv_usec = 1000;
+#endif
+		if (setsockopt(this->sock, SOL_SOCKET, SO_RCVTIMEO, (char*)&timeout, sizeof(timeout)) < 0)
 		{
+#ifdef _WIN32
 			int err = WSAGetLastError();
 			Log::FormatLine(LOG_ERROR, tag, "ERROR: Failed to set timeout. (Error code %i)", err);
-		}
 #else
-		struct timeval tv;
-		tv.tv_sec = 0;
-		tv.tv_usec = usTimeOut;
-		setsockopt(this->sock, SOL_SOCKET, SO_RCVTIMEO, (char *)&tv, sizeof(struct timeval));
+			Log::WriteLine(LOG_ERROR, tag, "ERROR: Failed to set timeout.");
 #endif
+		}
 	}
 
 	UDPSocket::~UDPSocket()
@@ -87,11 +90,9 @@ namespace XPC
 	int UDPSocket::Read(unsigned char* dst, int maxLen, sockaddr* recvAddr) const
 	{
 		socklen_t recvaddrlen = sizeof(*recvAddr);
-		int status = 0;
 
-#ifdef _WIN32
-		// Windows readUDP needs the select command- minimum timeout is 1ms.
-		// Without this playback becomes choppy
+		// For Read, use the select command - minimum timeout of 0 makes it polling.
+		// Without this, playback may become choppy due to process blocking
 
 		// Definitions
 		FD_SET stReadFDS;
@@ -103,27 +104,40 @@ namespace XPC
 		FD_SET(sock, &stReadFDS);
 		FD_ZERO(&stExceptFDS);
 		FD_SET(sock, &stExceptFDS);
+
+		// Set timeout period for select to 0 to poll the socket
 		tv.tv_sec = 0;
-		tv.tv_usec = 250;
+		tv.tv_usec = 0;
 
 		// Select Command
-		int result = select(-1, &stReadFDS, (FD_SET *)0, &stExceptFDS, &tv);
-		if (result == SOCKET_ERROR)
+		int status = select(-1, &stReadFDS, (FD_SET *)0, &stExceptFDS, &tv);
+		if (status < 0)
 		{
+#ifdef _WIN32
 			int err = WSAGetLastError();
 			Log::FormatLine(LOG_ERROR, tag, "ERROR: Select failed. (Error code %i)", err);
+#else
+			Log::WriteLine(LOG_ERROR, tag, "ERROR: Select failed.");
+#endif
+			return -1;
 		}
-		if (result <= 0) // No Data or error
+		if (result == 0)
 		{
+			// No data
 			return -1;
 		}
 
 		// If no error: Read Data
 		status = recvfrom(sock, (char*)dst, maxLen, 0, recvAddr, &recvaddrlen);
+		if (status < 0)
+		{
+#ifdef _WIN32
+			int err = WSAGetLastError();
+			Log::FormatLine(LOG_ERROR, tag, "ERROR: Receive failed. (Error code %i)", err);
 #else
-		// For apple or linux-just read - will timeout in 0.5 ms
-		status = (int)recvfrom(sock, dst, 5000, 0, recvAddr, &recvaddrlen);
+			Log::WriteLine(LOG_ERROR, tag, "ERROR: Receive failed.");
 #endif
+		}
 		return status;
 	}